Photo-oxidative degradation of waste expanded polystyrene using a pool disinfectant: TCCA as a low-cost photo-HAT reagent

Abstract

The low recycling rates (<1 %) of expanded polystyrene (EPS) and its tendency to fragment into microplastics pose significant environmental challenges, driving the need for cost-effective chemical upcycling strategies. Here, we demonstrate photochemicaldegradation of waste EPS using trichloroisocyanuric acid (TCCA), a common inexpensive (∼$1/kg) pool disinfectant, under UV-A irradiation and oxygen (O2) atmosphere in green ethyl acetate solvent. TCCA serves as Hydrogen Atom Transfer (HAT) reagent, generating reactive chlorine species (RCS) upon photolysis that abstract benzylic C–H bonds in polystyrene, initiating oxidative degradation. GPC results reveal that under optimized conditions, EPS is reduced from 83 kDa to ∼2 kDa (M n), yielding low-molecular-weight oxygenated oligomers along with value-added aromatic molecules (mainly acetophenone and benzoic acid), quantified by UPLC-TOF. Real-time NMR monitoring and control experiments indicate that photogenerated RCS dominate the degradation mechanism with minor contribution from reactive oxygen species (ROS). The demonstrated photochemical method offers a practical benefit, as the byproduct cyanuric acid, known to act as a strong oxygenation inhibitor, precipitates in ethyl acetate. This straightforward, metal-free approach is an economically viable route to transform waste EPS into valuable chemical feedstocks under mild conditions.